Over the years, APCs such as Dendritic Cells (DCs) have emerged as key players in orchestrating immune responses and in particular in inducing primary responses in patients in general. Nowadays, DCs can be generated on a large scale in closed systems, yielding sufficient numbers of cells for use in clinical trials. Simultaneously, antigens derived from infectious microorganisms and many different tumor-associated antigens, which are either selectively or preferentially expressed by tumor cells have been identified. Also, a whole range of strategies to load DCs with such antigens have been designed. Together, these findings enabled the start of clinical studies with antigen-loaded DCs in cancer patients and in patients suffering from infections. Nonetheless, satisfying immunological responses and clinical outcomes are difficult to achieve.
One major problem using DCs loaded with a target-specific antigen as APCs is that they are insufficient for eliciting a strong immune response both in vitro and in vivo. One cause of this insufficient immunostimulation is the complicated in vitro manipulation of the DCs prior to their use, leading to loss of their characteristic properties such as secretion of cytokines and other factors triggering immune responses. Another problem is that artificially made DCs often do not express the necessary cellular markers on their cell-surface needed to activate a T-cell response to the target-specific antigen presented by the DCs thereby overcoming the often occurring T-cell tolerance towards the target-specific antigens.
Different approaches can be used to transfect DCs including an extensively studied ex vivo approach in which DCs are modified ex vivo with subsequent adoptive transfer of transfected DCs to the patient. Direct administration of mRNA and uptake in vivo is a more recent approach that has advantages over the ex vivo approach. The most important advantage is that it allows a decrease in the amount of manipulation steps and time. When antigens are administered in vivo, for example into the lymph nodes through intranodal injection, they are not easily presented by APCs such as DCs in an immunostimulatory fashion. When combining the in vivo approach with a maturation stimulus, for example through the stimulation of the DCs with e.g. LPS in order to mature them, this furthermore usually blocks the uptake and presentation of the actual antigens, resulting in poor antigen presentation of the target antigens.
It is therefore the object of the current invention to provide a solution to the above stated problems.